The demand for frozen or refrigerated goods has resulted in a concomitant demand for refrigerated storage facilities. A variety of refrigerated storage facilities have been used to store refrigerated goods.
For example, freezers have been equipped with doors that provide access to such freezers from loading docks or other adjacent spaces. Such doors can be opened and closed manually or automatically to allow vehicle and pedestrian traffic access to the freezers. Such doors are intended to permit refrigerated goods to be moved into and out of the freezers with increased energy efficiency.
However, traffic through such doors is frequently heavy, particularly at peak periods of the day. Accordingly, during these peak periods, the doors are necessarily open for large amounts of time, and many doors are kept open continuously during such peak traffic periods. Such open doors can present problems both with regard to the operation and maintenance of refrigeration equipment and with regard to the productivity and safety of the facility.
As has been recognized, an open door to a refrigerated space permits the heavier refrigerated air to flow out of the refrigerated space through the lower portion of the door opening and a more or less equal mass of warm humid air to flow inward through the upper portion of the door opening. The warm air entering the refrigerated space is typically referred to as infiltration air, and the cold air escaping the refrigerated space is typically referred to as exfiltration air.
When a warm, more humid air mass encounters a cold, less humid air mass, precipitation commonly occurs. This precipitation is in the form of water droplets on the warm side of the door and air born ice crystals in the freezer.
Air born ice crystals in the freezer is usually visible as haze, while visible fog frequently appears on the warm side of the door as cold air escapes from the lower portion of the door opening and mixes with the warmer humid outside air. Fog can obstruct the vision of personnel, including vehicle operators, working in the area. In addition, water droplets on the warm side of the door frequently causes wet slippery floors in the vicinity of the door with consequent hazards not only to personnel but also to equipment and material.
Air born ice crystals in the freezer result in frost or snow accumulation on ceilings, walls, freezer room appurtenances, and on the goods stored in the room. Frost can grow to many inches in thickness and can result in icy floors that present extremely slippery and hazardous conditions for personnel and for vehicles such as forklift trucks. Further, air born ice crystals may be drawn into the refrigeration equipment and produce premature clogging of the coils of the equipment, thereby reducing the refrigeration effect and adding to the burden of defrosting the coils. The result is a substantial reduction in refrigeration efficiency and may require installation of additional evaporator coils or oversized refrigeration equipment.
Many attempts have been made to reduce air exchange through open doors of refrigerated spaces. One common approach employs an air curtain across the doorway opening. The forced flow of relatively high velocity air of the air curtain across the opening serves to restrict the normal air exchange that results due to the temperature differential across the doorway. This forced flow of relatively high velocity air also serves to mix any cold air escaping from the freezer through the air curtain with the air in the high velocity air stream. Thus, the escaping cold air is diluted which reduces the precipitation rate.
It is also known to heat the air used in such air curtains thereby further reducing precipitation both inside and outside the refrigerated space.
Air curtains, however, are expensive to install and use, and do not of themselves result in energy efficient and low frost operation.
Air conditioned vestibules and anterooms have also been used. The conditions in these vestibules and anterooms can be controlled somewhere between outside air conditions and the conditions inside the freezer in order to reduce the water and frost problems described above. However, vestibules and anterooms have not been also controlled so as to efficiently use energy and minimize frost in the freezer.
Air curtains have been combined with vestibules and anterooms. Such arrangements, while effective in reducing precipitation in both the freezer and the vestibule or anteroom, are expensive to install.
Strip doors have also been used to restrict the flow of air through an open door of a freezer. Such strip doors typically employ transparent vinyl strips. These strips part when personnel and vehicles pass through them, and they then quickly fall back into place when personnel and vehicles clear them. These strips, therefore, act as an air flow barrier.
However, strip doors do not sufficiently reduce frost in the freezer and the consumption of energy. The use of strip doors is also objectionable because the strips tend to become less transparent with use and age, and may, therefore, obstruct vision. Further, frost or fog condensation on the strip surfaces not only obstructs vision, but the wet, cold surfaces are generally considered objectionable by personnel passing through the door. The relatively heavy plastic strips can also drag lightweight items such as empty cartons from material handling equipment.
The present invention overcomes one or more of these or other problems.